When developing new material, especially heat conductive material, the heat conductivity of the material needs to be measured. When designing a heat dissipation device for electronic devices, the designer needs to know the heat conductive capability of the material of the heat dissipation device. Precisely measuring heat conductivity of the material is the key of the design.
In early times, the heat conductivity of a material is measured via sandwiching a specimen made of the material between a heat source and an object with a lower temperature. The heat generated by the heat source flows through the specimen to the object with lower temperature. A temperature gradient ΔT exists between two opposite ends of the specimen. The distance between the two opposite ends of the specimen ΔX can be measured. Assuming that all of the heat generated by the heat source flow through the specimen, the heat energy Q of the heat flow flowing through the specimen is equal to the heat energy Q′ generated by the heat source. The heat energy Q′ generated by the heat source is calculated according to the equation as follows:Q′=αI2R
R is the resistance value of a thermal resistor embedded in the heat source, I represents the electric current flowing through the thermal resistor, and α is a ratio of electrical power converted to heat energy of the thermal resistor. The heat conductivity K of the material of the specimen can be calculated according to the equation as follows:K=q*ΔX/ΔTq represents heat flow which is the rate at which heat energy Q flows through the specimen per square meter, in W/m2.
In the above method, the specimen firmly contact with one face of the heat source. The other faces of the heat source are heat insulated by a layer of insulation material covered thereon in order to ensure all of the heat generated by the heat source flow through the specimen. However, the insulation capability of the insulation material, such as alumina, is limited. Some of the heat generated by the heat source is inevitably dissipated through the other faces which do not contact the specimen. That means, the heat energy Q flowing through the specimen is not equal to the heat energy Q′ generated by the heat source. Thus, the value of the heat flow q flowing through the specimen exists an inaccuracy which results in the calculated value of the heat conductivity K of the material of the specimen existing an inaccuracy.